Polymers are used as additives in asphalts and bitumens for processing in roads or industry, either for improving their use characteristics by modifying the hot rheological properties, or for improving their physicochemical properties (cold brittleness, toughness, flexibility, stability, thermal susceptibility, mechanical resistance to shocks, vibrations, abrasions, etc.).
In general, the polymers used are thermoplastics (olefin copolymers or polymers), rubbers and in particular thermoplastic elastomers (multiblock copolymers of diolefins and styrene), or to a lesser extent, thermosetting resins (polyurethanes, epoxy resin, phenol formaldehyde). According to the prior art, these polymers can be used alone or in mixed form. For example, it has been proposed to recycle as additives for bitumens, manufacturing waste materials (waxes of polyethylene, atactic polypropylene, polyvinyl alcohol, powdered vulcanized rubber waste, etc.) or plastic waste obtained from domestic refuse and more particularly plastic packs. In the latter case, the mixtures of polymers essentially contain polyolefins, polyvinyl chloride, polystyrene and polyethylene terephthalate.
Polymers are added in small quantities (generally 2 to 10% by weight) to bitumens, in the form of "simple" mixtures involving no chemical reaction or interaction between the constituents, or in the form of "complex" mixtures involving a chemical reaction or interaction between the polymer and certain constituents of the bitumen (asphaltenes, malthenes, resins, etc.), optionally in the presence of a third constituent (catalyst or reagent). Usually the polymers are dispersed in the solid or melted state in a previously heated bitumen excess and, after stirring, the mixtures are used as they are in the melted state, or cooled to the solid state, and are optionally ground or granulated. Certain processes for the production of a mixture in the melted state of olefin polymer-added road-making bitumens, recommend the addition of at least 5 to 30% by weight of mineral particles, which accelerate the dissolving of the polymer in the bitumen (cf. e.g. U.S. Pat. No. 3,336,252, published Aug. 15, 1967). U.S. Pat. No. 4,028,293 published on Jun. 7, 1977 claims the production of a bitumen-containing material, which is more particularly used in the road-making and building fields and which is obtained by the high temperature reaction (at least at 180.degree. C.) of a mineral compound such as sand or gravel with a polymer or a mixture of polymers obtained from domestic or household refuse. The resulting mixture is then added hot to the bitumen and cooled. A major disadvantage of this method is the final cost of the operation, which involves a high temperature preheating of a large amount of mineral material prior to the addition of the polymer or polymers.